[Feature] Support for Preserving X-Forwarded-Host in AKS Application Routing Add-on

[Soren-Knudsen]

Is your feature request related to a problem? Please describe.
The AKS Application Routing add-on currently does not support the annotation of `nginx.ingress.kubernetes.io/use-forwarded-headers. In a standard self-managed NGINX ingress controller, this annotation allows the correct processing of forwarded headers—especially X-Forwarded-Host. Without support for this annotation, our applications receive internal DNS values rather than the intended public domain, causing issues with authentication, logging, and routing.

Describe the solution you'd like
I would like the AKS Application Routing add-on to support the nginx.ingress.kubernetes.io/use-forwarded-headers annotation. This would enable the managed NGINX ingress controller to preserve and correctly forward standard headers like X-Forwarded-Host, X-Forwarded-Proto, and X-Forwarded-For. Allowing this configuration would ensure that the original request information from upstream (e.g., Azure Front Door) is maintained, without needing non-standard workarounds or a custom ingress controller.

Describe alternatives you've considered
Currently, the alternatives include:

• Configuring Azure Front Door to set custom headers (e.g., a non-standard header) and modifying application logic to rely on them.
• Deploying a self-managed NGINX ingress controller with full configuration control, which increases operational overhead and deviates from the managed experience offered by the application routing add-on.

Both alternatives introduce extra complexity and are less desirable than a native solution within the add-on.

Additional context
Accurate forwarding of headers is essential for correct authentication, logging, and routing in enterprise scenarios. This feature would significantly improve the usability of the managed Application Routing add-on, making it a more robust option for production workloads that depend on precise client and request information.